Racemization of Optically Active Aromatic N-Acetylamino Acids and Asymmetric Transformation of N-Acetyl-2-(4-hydroxyphenyl)glycine via Salt Formation with Optically Active α-Methylbenzylamine

Article abstract of DOI:10.1246/bcsj.65.965

The racemization rates of N-acetyl-(S)-tyrosine, N-acetyl-(S)-phenylalanine, N-acetyl-(R)-2-(4-hydroxyphenyl)glycine <(R)-AcHpg>, N-acetyl-(R)-2-phenylglycine, and N-acetyl-(S)-alanine were measured by use of (RS)-α-methylbenzylamine <(RS)-MBA> as base-catalyst.The first-order rate constant for racemization tended to increase with an increase in the polar substituent constant of the N-acetylamino acid side chain.The racemization appeared to be subject to the inductive effect by the side chain.An asymmetric transformation of (RS)-AcHpg by using (R)-MBA, based on the result of racemization, gave an optically pure salt of (R)-AcHpg with (R)-MBA by successive use of the filtrate as the solvent.Optically pure (R)-2-(4-hydroxyphenyl)glycine <(R)-Hpg> was separated from the salt in 87-90percent yield based on the starting (RS)-AcHpg.In addition, the asymmetric transformation of (R)-AcHpg was achieved by using (S)-MBA to give optically pure (S)-Hpg in 80percent yield after purification of the salt of (S)-AcHpg with (S)-MBA followed by hydrolysis.